1. Field of the Invention
The present invention relates in general to a semiconductor technology. More particularly, it relates to a method of forming inter-metal dielectric (IMD) to prevent voids or seams formed in the dielectric.
2. Description of the Related Art
Conductive materials, semiconductors, and insulating materials are widely applied in the integrated circuit (IC) industry, and the main technology for IC industry includes thin film deposition, photolithography, and etching. Thin film deposition deposits the materials as mentioned above onto a wafer to be fabricated. Photolithography reproduces desired device or circuit patterns in the photoresist layer over the thin films. Etching transfers the device or circuit patterns onto the thin films through the patterned photoresist layer, to form devices such as transistors or capacitors on the wafer.
After the devices or circuits are finished, metal wires connecting each device or circuit must be formed, referred to as metallization. In metallization, a nonconductive layer of dielectric material, such as silicon dioxide is often formed between the metal wires or devices. This dielectric layer may protect metal wires from physical or chemical damage, insulate metal wire from other wires, and insulate devices. Typically, this dielectric layer is called inter-layer dielectric (ILD) and inter-metal dielectric.
As semiconductor device geometries continue to decrease in size to provide more devices per fabricated wafer and faster devices, line width of the metal wires for connecting each device and the spacing between the metal wires has been reduced. However, as the spacing or gaps between these metal wires decrease, it becomes more difficult to fill the gap with the dielectric material because of increasing the aspect ratio of the gap.
Accordingly, the gap cannot be filled fully with the dielectric material by physical vapor deposition (PVD) or chemical vapor deposition (CVD). Particularly, as the aspect ratio of the gap exceeds 3.5, voids or seams are formed in the gap during dielectric filling. As a result, the reliability of the devices is reduced.
Accordingly, an object of the invention is to provide a method of forming inter-metal dielectric to avoid voids or seams in the dielectric in the gap by reducing the aspect ratio of the gap through a double dielectric filling process.
To achieve these and other advantages, the invention provides a method of forming inter-metal dielectric. First, a substrate having a patterned metal layer thereon is provided, in which the patterned metal layer has at least one opening to expose the substrate. The opening has an aspect ratio of 3.5xcx9c4.5. Next, a conformable protective layer is formed over the patterned metal layer and the opening. Next, the opening is filled with a first dielectric layer, and voids are formed in the upper portion of the first dielectric layer due to the high aspect ratio opening. Thereafter, the first dielectric layer is etched to leave the first dielectric layer with a predetermined height in the opening without voids therein. Finally, a second dielectric layer is formed on the first dielectric layer to completely fill the opening.
The patterned metal layer is aluminum, the protective layer is silicon nitride, and the first and the second dielectric layer are high density plasma oxide. Moreover, the predetermined height is 1000xcx9c1400 xc3x85.